Radio frequency slot antenna

ABSTRACT

A stripline slotted array antenna is disclosed wherein the radiating efficiency and bandwidth are improved by including in each radiating element a pair of adjacent radiating slots. The antenna includes center conductor circuitry separated from a pair of ground plane elements, one of which is the radiating face of the antenna and one of which is the back plate of the antenna. The pair of slots is formed in the radiating face of the antenna. The pair of radiating slots is disposed adjacent to an end portion of the center conductor circuitry, one being coupled to an electric field existing between the end of such circuitry and the back plate and the other one of such pair of radiating slots being coupled to an electric field existing between the center conductor circuitry and the radiating face of the antenna.

United States Patent [191 Plunk et a]. i

[451 Aug. 27, 1974 RADIO FREQUENCY SLOT ANTENNA Inventors: Troy E.Plunk, Bedford; Richard J.

Laramee, Dedham, both of Mass.

Assignee: Raytheon Company, Lexington, Mass. 7

Filed: May 23, 1973 A ,ppl. No.: 363,238

vs. C]. 343/770, 343/846, 333/84 M 1m. (:1. H0lq 13/10 Field of Search343/769, 770, 771, 846;

References Cited UNITED STATES PATENTS Joseph D. Pannone; Philip J.McFarland [57] ABSTRACT A stripline slotted array antenna is disclosedwherein the radiating efficiency and bandwidth are improved by includingin each radiating element a pair of adjacent radiating slots. Theantenna includes center conductor circuitry separated from a pair ofground plane elements, one of which is the radiating face of the antennaand one of which is the back plate of the antenna. The pair of slots isformed in the radiating face of the antenna. The pair of radiating slotsis disposed adjacent to an end portion of the center conductorcircuitry, one being coupled to an electric field existing between theend of such circuitry and the back plate and the other one of such pairof radiating slots being coupled to an electric field existing betweenthe center conductor circuitry and the radiating face of the antenna.

11 Claims, 2 Drawing Figures PAIENTEU Y H F I G. 2

BACKGROUND OF THE INVENTION This invention relates generally to radiofrequency antennas and more particularly to stripline slotted arrayantennas.

As is known in the art, stripline antennas are sometimes used in placeof waveguide antennas because of their relatively lighter weight andcompactness. Such stripline antennas generally include center conductorcircuitry separated from a pair of ground plane elements (one theradiating face of the antenna and the other the back plate of theantenna) by a dielectric material. The radiating face of such an antennagenerally includes an array-of radiating slots. The radiating slots arecoupled to the electric field existing between end portions of thecenter conductor circuitry of the stripline and the ground planeelements. One such stripline antenna is described in US. Pat. No.3,701,158, issued to Robert H. Johnson, Oct. 24, l972.

In the vicinity of each one of the radiating slots of known striplineantennas the electric field existing between the center conductorcircuitry and the radiating face is not balanced with the electric fieldexisting between the center conductor circuitry and the back plate. Suchunbalance causes energy to be reflected within the stripline, therebyreducing the radiating efficiency of the antenna by about 50 percent.One technique used to reduce reflections and thereby improve theradiating efficiency has been to electrically enclose the radiating slotwithin a high Q resonant cavity. Such a cavity may be formed by usingknown mode suppression posts, or pins, of conducting material adjacentto each radiating slot. A high Q resonant cavity of such nature, whileimproving the radiating efficiency of the antenna, reduces the operatingbandwidth of the antenna so that, generally, only a -15 percentvariation in operating frequency may be attained.

SUMMARY OF THE INVENTION With this backgroundof the invention in mind,it is an object of this invention to provide a stripline slotted arrayantenna having improved radiating efficiency and bandwidth.

The foregoing and other objects of the invention are attained generallyby providing, in a stripline slotted array antenna (including centerconductor circuitry separated from a pair of ground plate elements, oneof which is the radiating face of the antenna and one of which is theback plate of the antenna), an array of radiating elements, each onethereof terminating an end portion of the center conductor circuitry andincluding a pair of adjacent radiating slots formed in the radiatingface, one thereof being adjacent to the end of the center conductorcircuitry and coupled to an electric field existing between suchcircuitry and the back plate and the other one being coupled to anelectric fieldexisting between the center conductor circuitry and theradiating face.

BRIEF DESCRIPTION OF THE DRAWINGS i The foregoing features of thisinvention, as well as the invention itself, may be more fully understoodfrom the following detailed description read together with theaccompanying drawings, in which:

FIG. 1 is a plane frontal viewof a radio frequency an-. tenna accordingto the invention; and

FIG. 2 is a cross-sectional view of one of the radiating elements of theantenna of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIGS. 1 and 2,a stripline antenna 10 is shown to include center conductor circuitry 11separated from a pair of ground plane elements l2, 14 by a dielectricmaterial 16. Ground plane elements 12, 14 are herein sometimes referredto as the radiating face of the antenna and the back plate of theantenna, respectively. In particular, such antenna 10 is here fabricatedfrom two slabs of dielectric material, one having plated or depositedthereon a conducting material, here copper, to form the back plate 14 ofthe antenna and the other one having plated or deposited on portions ofsuch side thereof a conducting material, here copper, to form theradiating face of the antenna 10 and center conductor circuitry 11. Thetwo slabs are secured together by any suitable conventional means, suchas epoxy, not shown.

Antenna 10 includes an array of radiating elements 18 48 Each one of theradiating elements is identical in construction and each terminates anend portion of center conductor circuitry 11 (only the end portion 19,which terminates radiating element 18 being numbered). An exemplary oneof such radiating elements, here 18 includes a pair of radiating slots20, 22, here formed in the radiating face 12 by conventional etching ofportions of the conducting material making up such face. The pair ofradiating slots 20, 22 is surrounded by mode suppression pins 24. Suchmode suppression pins 24 are formed by drilling holes through theradiating face 12 and dielectric material 16 to the back plate 14, andby filling such holes with a conducting material, here copper. The modesuppression pins 24 are secured to the radiating face and to the backplate by any suitable means, here solder, not shown. However, such modesuppression pins 24 may be formed by providing holes through the antenna10 and by electroplating the walls of such holes. The mode suppressionpins 24 form a relatively low Q resonant cavity around the radiatingslots 20, 22. Because such a cavity forms no part of the presentinvention, the mode suppression pins 24 may be omitted. Includedintermediate the pair of radiating slots 20, 22 is a pair of additionalpins, 26, 28. Also included is an additional pin 29. Such pins 26, 28,29 are formed by drilling holes through the radiating face 12 and thedielectric material 16 of the upper dielectric slab to the centerconductor circuitry 11 and by filling such holes with a conductingmaterial, here copper, as shownin FIG. 2'or by the electroplatingprocess mentioned above in connection with pins 24.

The radiating elements 18 18 are here arranged in four sectors, orquadrants A, B, C, D, to configure antenna 10 as a monopulse antenna.The four quadrants are separated along dotted lines 30, as shown.

Each one of the four sectors includes seven radiating elements. Herequadrants A-D include radiating elements 181-187, lay-1814, 18 5-18 and1822-1823, respectively. Considering any one of the quadrants, sayexemplary quadrant A, center conductor circuitry 11 may be seen to beconnected with a terminal 32A, with seven branch lines (not numbered),the end portion of each one of such branches being adjacent to, andterminated by, a different one of radiating elements as shown. Itfollows, therefore, that each radiating element in quadrant A is coupledto terminal 32A. Thus, when antenna is used as a receiving antenna,radio frequency energy from an external source (not shown) irradiatingthe radiating elements 18 -18 in quadrant A is passed to terminal 32A.The equivalent is true for quadrants B-D and terminals 32B 32Drespectively. It follows then that by coupling terminals 32A 32D to aconventional monopulse arithmetic unit (not shown), the conventional sumand difference channels of a monopulse antenna may be obtained.

Referring again to FIG. 2, now in more detail, it may be observed thatan electric field may exist between the center conductor circuitry 11and the radiating face 12 (as indicated by arrows 34), and also anelectric field may exist between such circuitry and the back plate 14(as indicated by arrows 36). It may further be observed that radiatingslot is coupled to the electrical field existing between the radiatingface 12 and the center conductor circuitry 11 and radiating slot 22 iscoupled to the electric field existing between center conductorcircuitry 11 and back plate 14. To put it another way, pin 26 andportions of center conductor circuitry 11 and radiating face 12 may beviewed as being a feed for radiating slot 20 whereas pins 28, 29, backwall 14 and the end of center conductor circuitry 11 may be viewed asbeing a feed for radiating slot 22. Therefore, the electric fields inthe pair of dielectric slabs are balanced. Reflections within theantenna, which normally result without such radiating slot 22, arereduced. By separating the radiating slots 20, 22 by an integralmultiple (half wavelength) N2 (where A is the nominal operatingwavelength of the antenna 10 in the dielectric material 16) radiofrequency energy fed to such slots will be in phase. On the other hand,by separating such slots by a distance equal to an integral multiple ofA in the dielectric material 16, such energy will be 180 out of phase"along the boresight axis of the antenna.

Having described a preferred embodiment of this invention, it is nowevident that other embodiments incorporating the concepts may be used.For example, in reference to FIG. 1, the shape of radiating slots 20, 22may take other forms to provide proper impedance matching. For example,the shape of such slots as herein shown provides a capacitive impedancematching. Further, while a monopulse antenna has been shown it isunderstood that other antenna configurations, as a beacon antenna, mayuse the inventive concepts herein described. Further, the separationbetween the pair of radiating slots 20, 22 may be selected to providefor one of a variety of desired radiation patterns. It is felt,therefore, that this invention should not be restricted to its disclosedembodiments but rather should be limited only by the spirit and scope ofthe appended claims.

What is claimed is:

1. In a stripline slotted array antenna including center conductorcircuitry separated from a pair of ground plane elements, one of whichis the radiating face of the antenna and one of which is the back plateof the antenna, an array of radiating elements, each one thereofterminating anend portion of the center conductor circuitry andcomprising:

a. a first radiating slot, formed in the radiating face,

disposed adjacent to the end of the center conductor circuitry andcoupled to an electric field existing between such circuitry and theback plate of the antenna; and

b. a second radiating slot, formed in the radiating face, disposedadjacent to, and totally separated from, the first slot by a portion ofthe radiating face, such second radiating slot being coupled to anelectric field existing between the center conductor circuitry and theradiating face of the antenna.

2. The radiating element recited in claim 1 including a. a firstconducting material disposed intermediate the first and second radiatingslots and extending from the radiating face to the center conductorcircuitry, such first conducting material, center conductor circuitryand radiating face being arranged to form a feed for the secondradiating slot; and

b. a second conducting material disposed outside both the firstradiating slot and the end of the center conductor circuitry andextending from the radiating face to the back plate, such secondconducting material, center conductor circuitry, first conductingmaterial, and back plate being arranged to form a feed for the firstradiating slot.

5. The radiating element recited in claim 1 wherein the first radiatingslot and the second radiating slot are separated by an integral numberof )t/2 where A is the operating wavelength of the antenna.

6. In a stripline slotted array antenna including center conductorcircuitry separated from a pair of ground plane elements, one of whichis the radiating face of the antenna and one of which is the back plateof the antenna, an array of radiating elements, each one thereofterminating an end portion of the center conductor circuitry andcomprising: i

a. a first radiating slot, formed in the radiating face,

disposed adjacent to the end of the center conductor circuitry andcoupled to an electric field existing between such circuitry and theback plate of the antenna;

b. a second radiating slot, formed in the radiating face, disposedadjacent to the first slot and coupled to an electric field existingbetween the center conductor circuitry and the radiating face of theantenna; and,

c. a conducting material disposed outside the first radiating slot andextending from the radiating face to the back plate of the antenna.-

7. The radiating element recited in claim 6 including:

a. a first conducting material disposed intermediate the first andsecond radiating slots and extending from the radiating face to thecenter conductor circuitry, such first conducting material, centerconductor circuitry and radiating face being arranged to form a feed forthe second radiating slot; and

b. a second conducting material disposed outside both the firstradiating slot and the end of the center conductor circuitry andextending from the radiating face to the back plate, such secondconducting material, center conductor Circuitry, first conductingmaterial, and back plate being arranged to form a feed for the firstradiating slot.

8. In a stripline slotted array antenna including center conductorcircuitry separated from a pair of ground plane elements, one of whichis the radiating face of the antenna and one of which is the back plateof the antenna, an array of radiating elements, each one thereofterminating an end portion of the center conductor circuitry andcomprising:

a. a first radiating slot, formed in the radiating face,

disposed adjacent to the end of the center conductor circuitry andcoupled to an electric field existing between such circuitry and theback plate of the antenna; and

b. a second radiating slot, formed in the radiating face, disposed anintegral multiple of M2, where A is the operating wavelength of theantenna, from the first slot and coupled to an electric field existingbetween the center conductor circuitry and the radiating face of theantenna.

9. The radiating element recited in claim 8 including conductingmaterial disposed intermediate the first and second radiating slots andextending from the radiating face to the center conducting circuitry.

10. The radiating element recited in claim 9 including an additionalconducting material disposed outside the first radiating slot andextending from the radiating face to the back plate of the antenna.

11. The radiating element recited in claim 8 includmg:

a. a first conducting material disposed intermediate the first andsecond radiating slots and extending from the radiating face to thecenter conductor circuitry, such first conducting material, centerconductor circuitry and radiating face being arranged to form a feed forthe second radiating slot; and

b. a second conducting material disposed outside both the firstradiating slot and the end of the center conductor circuitry andextending from the radiating face to the back plate, such secondconducting material, center conductor circuitry, first conductingmaterial, and back plate being arranged to form a feed for the firstradiating slot.

1. In a stripline slotted array antenna including center conductorcircuitry separated from a pair of ground plane elements, one of whichis the radiating face of the antenna and one of which is the back plateof the antenna, an array of radiating elements, each one thereofterminating an end portion of the center conductor circuitry andcomprising: a. a first radiating slot, formed in the radiating face,disposed adjacent to the end of the center conductor circuitry andcoupled to an electric field existing between such circuitry and theback plate of the antenna; and b. a second radiating slot, formed in theradiating face, disposed adjacent to, and totally separated from, thefirst slot by a portion of the radiating face, such second radiatingslot being coupled to an electric field existing between the centerconductor circuitry and the radiating face of the antenna.
 2. Theradiating element recited in claim 1 including conducting materialdisposed intermediate the first and second radiating slots and extendingfrom the radiating face to the center conducting circuitry.
 3. Theradiating element recited in claim 2 including an additional conductingmaterial disposed outside the first radiating slot and extending fromthe radiating face to the back plate of the antenna.
 4. The radiatingelement recited in claim 1 including: a. a first conducting materialdisposed intermediate the first and second radiating slots and extendingfrom the radiating face to the center conductor circuitry, such firstconducting material, center conductor circuitry and radiating face beingarranged to form a feed for the second radiating slot; and b. a secondconducting material disposed outside both the first radiating slot andthe end of the center conductor circuitry and extending from theradiating face to the back plate, such second conducting material,center conductor circuitry, first conducting material, and back platebeing arranged to form a feed for the first radiating slot.
 5. Theradiating element recited in claim 1 wherein the first radiating slotand the second radiating slot are separated by an integral number oflambda /2 where lambda is the operating wavelength of the antenna.
 6. Ina stripline slotted array antenna including center conductor circuitryseparated from a pair of ground plane elements, one of which is theradiating face of the antenna and one of which is the back plate of theantenna, an array of radiating elements, each one thereof terminating anend portion of the center conductor circuitry and comprising: a. a firstradiating slot, formed in the radiating face, disposed adjacent to theend of the center conductor circuitry and coupled to an electric fieldexisting between such circuitry and the back plate of the antenna; b. asecond radiating slot, formed in the radiating face, disposed adjacentto the first slot and coupled to an electric field existing between thecenter conductor circuitry and the radiating face of the antenna; and,c. a conducting material disposed outside the first radiating slot andextending from the radiating face to the back plate of the antenna. 7.The radiating element recited in claim 6 including: a. a firstconducting material disposed intermediate the first and second radiatingslots and extending from the radiating face to the center conductorcircuitry, such first conducting material, center conductor circuitryand radiating face being arranged to form a feed for the secondradiating slot; and b. a second conducting material disposed outsideboth the first radiating slot and the end of the center conductorcircuitry and extending from the radiating face to the back plate, suchsecond conducting material, center conductor circuitry, first conductingmaterial, and back plate being arranged to form a feed for the firstradiating slot.
 8. In a stripline slotted array antenna including centerconductor circuitry separated from a pair of ground plane elements, oneof which is the radiating face of the antenna and one of which is theback plate of the antenna, an array of radiating elements, each onethereof terminating an end portion of the center conductor circuitry andcomprising: a. a first radiating slot, formed in the radiating face,disposed adjacent to the end of the center conductor circuitry andcoupled to an electric field existing between such circuitry and theback plate of the antenna; and b. a second radiating slot, formed in theradiating face, disposed an integral multiple of lambda /2, where lambdais the operating wavelength of the antenna, from the first slot andcoupled to an electric field existing between the center conductorcircuitry and the radiating face of the antenna.
 9. The radiatingelement recited in claim 8 including conducting material disposedintermediate the first aNd second radiating slots and extending from theradiating face to the center conducting circuitry.
 10. The radiatingelement recited in claim 9 including an additional conducting materialdisposed outside the first radiating slot and extending from theradiating face to the back plate of the antenna.
 11. The radiatingelement recited in claim 8 including: a. a first conducting materialdisposed intermediate the first and second radiating slots and extendingfrom the radiating face to the center conductor circuitry, such firstconducting material, center conductor circuitry and radiating face beingarranged to form a feed for the second radiating slot; and b. a secondconducting material disposed outside both the first radiating slot andthe end of the center conductor circuitry and extending from theradiating face to the back plate, such second conducting material,center conductor circuitry, first conducting material, and back platebeing arranged to form a feed for the first radiating slot.